Transient electrical conductivity of nonequilibrium carriers excited by subpicosecond optical pulses in GaAs

Vengurlekar, A. S.; Jha, Sudhanshu S.
August 1987
Applied Physics Letters;8/3/1987, Vol. 51 Issue 5, p323
Academic Journal
We calculate the time-dependent electrical conductivity σ(t) for the nonequilibrium carriers excited by a subpicosecond laser pulse in a polar semiconductor like GaAs. The photoexcited carriers are assumed to relax towards equilibrium by emitting longitudinal optical (LO) phonons in a cascade via the strong Fröhlich interaction. We show that σ(t), obtained in the picosecond time domain, has a highly nonlinear time evolution. It develops a pronounced dip, with its value becoming negative, whenever the generated low density carrier distribution is sharply peaked initially at energy ε[bar_over_tilde:_approx._equal_to]mhωLO, m=integer, hωLO being the long wavelength LO phonon energy.


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